When high pressure hydraulic lines are bent to shape as is normally required for installation, the bent portion of the line takes on an oval shape. This ovality is indicated by the difference between major and minor diameters of the lines. Excessive ovality indicates a weakening of the line that calls for rejection. One method of determining ovality of bent tubing is to use caliper type go-no-go gauges on the major and then on the minor diameters; which is time consuming, and requires rechecking.
U.S. Pat. No. 3,303,572 to T. Vreeland, Jr. shows a diameter gauge, for placement over the end of a member to be measured, with a pair of radially movable probes at 90 degrees from each other. A spring extends 270 degrees around the gauge with ends of the spring fastened to the probes. As the probes move it sets up a strain in the spring; which is sensed by a pair of strain gauge elements located on the spring to determine the average diametrical measurements.
U.S. Pat. No. 2,677,125 to Pistoles shows a snap type gauge for measuring across a diameter and indicating tolerance limits by use of lights.